The present invention relates to a series of new carbapenem compounds, to a process for preparing these compounds and to compositions containing the compounds.
The penicillins form a well-known class of antibiotics, which have found considerable use in human and animal therapy for many years. Chemically, the penicillins have in common a .beta.-lactam structure, commonly referred to as "penam", which may be represented by the following formula: ##STR4##
However, although the penicillins still form a valuable weapon in the pharmaceutical armory, the development of new, and often penicillin-resistant, strains of pathogenic bacteria has increasingly made it necessary to search for new types of antibiotic.
Recently, some interest has been shown in compounds having a carbapenem structure, that is compounds having a carbon atom in place of the sulphur atom at the 1-position and having a double bond between the carbon atoms in the 2- and 3-positions of the basic penam structure. The carbapenem structure may be represented by the following formula: ##STR5##
These penam and carbapenem structures form the basis for the semi-systematic nomenclature of the penicillin derivatives and this nomenclature is generally accepted by those skilled in the art throughout the world and is used herein. The numbering system employed herein is that illustrated on the above formulae.
Of the known carbapenem derivatives, the best known is a compound called "thienamycin", which may be represented by the following formula: ##STR6## Although thienamycin is known to have remarkably potent and broad antibacterial activity, its chemical stability in the human body is poor, which restricts its practical use. Various attempts have, therefore, been made to modify the chemical structure of thienamycin in order to improve its chemical stability whilst maintaining its superior activity.
One class of compound which has been prepared in an attempt to overcome the stability problem of thienamycin has a heterocyclylthio group at the 2-position and compounds of this type are described in European Patent Specifications No. 1627 and No. 17992, whilst processes for preparing compounds of this type are described in European Patent Specifications No. 38869 and No. 40408 and in Japanese Patent Specification Kokai (i.e. published but unexamined) No. 156281/81.
We have now discovered a limited class of compounds which, whilst structurally similar to those disclosed in European Patent Specification No. 17992, have much improved antibacterial activity, especially in vivo activity, compared with the compounds disclosed in European Patent Specification No. 17922.